Effect of prolonged, submaximal exercise and carbohydrate ingestion on monocyte intracellular cytokine production in humans

Abstract

The present study was undertaken to examine the effect of exercise and carbohydrate (CHO) ingestion on intracellular monocyte cytokine production. Subjects performed 2 h of cycling at 70 % peak pulmonary O2 uptake (VO2,peak) while ingesting either an 8 % CHO beverage or a sweet placebo. Whole blood was incubated with (stimulated) or without (spontaneous) lipopolysaccharide (LPS) and surface stained for monocyte surface antigens. The cells were permeabilised, stained for intracellular cytokines and analysed using flow cytometry. Exercise had no effect on the number of monocytes spontaneously producing cytokines, but the number of stimulated IL-1alpha-, TNF-alpha- and IL-6-positive monocytes were elevated (P < 0.01) immediately post-exercise and 2 h post-exercise. These stimulated cells produced less (P < 0.05) TNF-alpha immediately post-exercise, and less (P < 0.05) TNF-alpha and IL-1alpha 2 h post-exercise. There was a small, but significant increase (P < 0.05) in the plasma IL-6 concentration immediately post-exercise. Exercise resulted in an elevation (P < 0.01) in the plasma adrenaline concentration in the placebo trial, and ingestion of CHO attenuated this increase. CHO ingestion had no effect on monocyte cytokine production, plasma IL-6 or circulating leukocyte numbers. These data suggest that circulating monocytes are not the origin of increased levels of plasma IL-6 during exercise: prolonged cycling exercise increased the number of monocytes producing cytokines upon stimulation, but these cells produced less cytokines post-exercise. In addition, attenuation of plasma adrenaline levels had no effect on plasma IL-6 or monocyte cytokine production.

Figure 1. Number of IL-6-positive cells

Spontaneous (top) and LPS-stimulated (bottom) CD33⁺/IL-6⁺ cells prior to (Pre), immediately following (Post), and 120 min into recovery (2 h post) from 2 h of bicycle exercise with (CHO) or without (CON) the ingestion of an 8 % carbohydrate solution throughout exercise. Values are means ± s.e.m. (n = 6). ^† < 0·01, significantly different from pre-exercise values.

Figure 2. Number of TNF-α-positive cells

Spontaneous (top) and LPS-stimulated (bottom) CD33⁺/TNF-α⁺ cells prior to (Pre), immediately following (Post), and 120 min into recovery (2 h post) from 2 h of bicycle exercise with (CHO) or without (CON) the ingestion of an 8 % carbohydrate solution throughout exercise. Values are means ± s.e.m. (n = 6). ^†P < 0·01, significantly different from pre-exercise values.

Figure 3. Number of IL-6α-positive cells

Spontaneous (top) and LPS-stimulated (bottom) CD33⁺/IL-1α⁺ cells prior to (Pre), immediately following (Post), and 120 min into recovery (2 h post) from 2 h of bicycle exercise with (CHO) or without (CON) the ingestion of an 8 % carbohydrate solution throughout exercise. Values are means ± s.e.m. (n = 6). ^†P < 0·01, significantly different from pre-exercise values.

Figure 4. Plasma IL-6 concentration

Plasma IL-6 concentrations prior to (Pre), after 60 min (60 min), and immediately following (Post) 2 h of bicycle exercise with (CHO) or without (CON) the ingestion of an 8 % carbohydrate solution throughout exercise. Values are means ± s.e.m. (n = 6). ^†P < 0·01, significantly different from pre-exercise values.

Figure 5. Plasma adrenaline concentration

Plasma adrenaline concentrations prior to (Pre), after 60 min (60 min), and immediately following (Post) 2 h of bicycle exercise with (CHO) or without (CON) the ingestion of an 8 % carbohydrate solution throughout exercise. Values are means ± s.e.m. (n = 6). *P < 0·01, significantly different from pre-exercise values; ^†P < 0·01, significantly different from control.